A few months ago I had to take an overnight trip to LA from Denver, with 2 day's advance notice.

There are 5 airlines that fly this route (AA, DL, UA, WN and F9).

The price for the roundtrip in economy was $750 to $800 on all 5 airlines

A week later I had to do the same trip again, with less than 24 hours notice. Again the price for the roundtrip was $750 to $800 on all 5 airlines.

These were work trips, neither I nor my company batted an eye. Needed to be there and this was the price. Use of miles didn't enter into it.

For the most part, last minute trips are not price-sensitive travelers. Last minutes trips are "I've got to be there". Airlines know this.